Field of Invention
The present invention relates to an improved process for preparing N,O-triglycidyl aminophenol compounds. In one embodiment, the N,O-triglycidyl aminophenol compound is a compound of formula I or formula II, wherein R and R′ are each independently selected from the group consisting of hydrogen, C1-C6 alkyl, phenyl, cyclohexyl and cyclopentyl, R1, R2, R3, and R4 are each independently selected from the group consisting of hydrogen, halogen, and C1-C6 alkyl. More particularly, the present invention is related to a process for preparing N,O-triglycidyl aminophenol compounds which does not require at least one polar protic organic co-solvent in the first step of the process, wherein the first step involves the formation of a halohydrin adduct by reaction of at least one epihalohydrin with at least one aminophenol. In one embodiment, the aminophenol is at least one compound of formula III or formula IV.
Using the methods of the current invention, separation of unreacted epihalohydrin, which is used in molar excess over the other reactants represented by structures III and IV, from a polar protic organic solvent, such as ethanol, isopropanol, n-butanol and the like, is no longer required because the process does not require the use of a polar protic organic solvent.
The methods of the current invention are economical and have fewer steps than currently used processes. More particularly, this disclosure relates to an industrially useful, energy efficient manufacturing process for the synthesis of triglycidyl compound from 4-amino phenols.
Triglycidyl aminophenols are commercially useful as high performance epoxy resins. They are versatile compounds, and are also used in structural adhesives and matrix resins for composites used in aviation, coatings, and insulation materials.
Because the properties of composites are dependent upon matrix resins, much effort has been placed into developing new resins while simultaneously improving processes for their manufacture.
The present invention relates to an improved manufacturing process for multifunctional epoxy resins of structures I and II. Multifunctional epoxies capable of forming higher cross linked structures are in demand both in military and civil applications. High temperature resistance and chemical resistance is function of crosslink density of a cured resin system. High cross link density can be achieved through multi-functionality on epoxy resin or hardener agent.
Description of Prior Art
For high performance applications which require epoxy resins with high heat distortion properties, such as in the aviation industry, resins having a glycidyl group bonded to a nitrogen atom of an aromatic amine functional group are often preferred, and several manufacturing processes of these types of compounds have been reported in prior art.
U.S. Pat. No. 8,076,495 B2 discloses a process which involves reacting aromatic amines with about 0.8-1.0 equivalents of epichlorohydrin per amino hydrogen atom. Compounds containing an aromatic amine group are dissolved in an organic solvent, such as toluene, and reacted with epichlorohydrin. This method uses an exotic catalyst, such as hydrated lanthanum nitrate to, form the halohydrin adduct. This step is followed by a cyclisation step using caustic aqueous solution in the presence of a phase transfer catalyst. During the workup, more organic co-solvent (i.e., toluene) is added to remove residual inorganic salt. This process, however, has several drawbacks, including use limited to only one N-glycidyl amine compound and employing an expensive catalyst in the adduct formation step as well as a phase transfer catalyst in the cyclisation step. The process also requires an additional distillation step in order to separate the toluene from the epichlorohydrin for recycling and reuse of the reagents.
U.S. Pat. No. 4,540,769 discloses the synthesis of aromatic N-glycidyl amines by treating an amine having at least one but preferably two or more aromatic amino hydrogen atoms, with epichlorohydrin in the presence of a metal salt, which acts as a catalyst.
Both U.S. Pat. No. 8,076,495 B2 and U.S. Pat. No. 4,540,769 are silent on the epoxidation of compounds such as aminophenols, which have both an amine and hydroxyl functional group attached to an aromatic ring.
Epoxy resins with both hydroxyl and amine functional groups attached to an aromatic ring facilitate formation of N,O glycidyl ethers, resulting in more versatile epoxy resins with desirable characteristics, such as high distortion properties.
U.S. Pat. No. 2,951,825 discloses a method for producing a N,O glycidyl amine type epoxy compound, wherein p-aminophenol is reacted with epichlorohydrin at 25° C. for a period of 137 hrs in the presence of lithium hydroxide monohydrate catalyst and a participating organic co-solvent, such as ethyl alcohol, as solvent. However, this process results in lower product yield and productivity, and requires an additional step to separate the co-solvent from the reaction mixture.
Many of the prior art preparations of triglycidylaminophenols involve the use of a variety of alcohols, such as n-butanol, sec-butanol, n-pentanol, n-hexanol and iso-propanol, as an organic co-solvent in the step of forming the chlorohydrins adduct. Both CN 101139327 and JP 59044372 disclose the reaction of p-aminophenol and m-aminophenol with epichlorohydrin in an alcohol at 55° C. for 5 hrs. Other processes, such as those disclosed in JP 55033410 and JP 04139230, require the use of a lithium salt or a phase transfer catalyst in order to facilitate the reaction. For example, isobutanol was used as a co-solvent for producing aminophenol triglycidyl compounds in the presence of lithium hydroxide monohydrate catalyst.
In addition, the procedures of the prior art are silent on the recovery of the co-solvent, as well as the recycling and/or disposal of the reaction components, such as the epihalohydrin used for epoxidation, the organic co-solvent, and any inorganic catalyst used in the processes.
Another drawback of the prior art processes is the ability to maintain batch to batch identity and quality of the recovered mixed solvents. Moreover, the prior art processes require an additional step of fractionating the organic co-solvents from the epihalohydrin, making these processes more energy intensive.
There is a need in the art for improved and energy-efficient manufacturing processes for preparing N,O-triglycidyl aminophenols. The present invention satisfies this need in the art.